* Roman Zippel <[email protected]> wrote:
> Every time hrtimer_run_queues() is called, get_time() is called twice,
> which can be quite expensive, just reading xtime is much cheaper and
> does the same job (at least for the current low resolution timer, for
> high resolution timer we can something different later). Cache the
> expiry time in last_expired, so run_hrtimer_queue() doesn't has to
> calculate it (clock sources usually know when their expired).
>
> Signed-off-by: Roman Zippel <[email protected]>
>
> ---
>
> include/linux/hrtimer.h | 1 +
> kernel/hrtimer.c | 17 +++++++++++++----
> 2 files changed, 14 insertions(+), 4 deletions(-)
>
> Index: linux-2.6-git/include/linux/hrtimer.h
> ===================================================================
> --- linux-2.6-git.orig/include/linux/hrtimer.h 2006-02-12 18:33:07.000000000 +0100
> +++ linux-2.6-git/include/linux/hrtimer.h 2006-02-12 18:33:21.000000000 +0100
> @@ -89,6 +89,7 @@ struct hrtimer_base {
> ktime_t resolution;
> ktime_t (*get_time)(void);
> struct hrtimer *curr_timer;
> + ktime_t last_expired;
> };
>
> /*
> Index: linux-2.6-git/kernel/hrtimer.c
> ===================================================================
> --- linux-2.6-git.orig/kernel/hrtimer.c 2006-02-12 18:33:16.000000000 +0100
> +++ linux-2.6-git/kernel/hrtimer.c 2006-02-12 18:33:21.000000000 +0100
> @@ -541,7 +541,7 @@ int hrtimer_get_res(clockid_t which_cloc
> */
> static inline void run_hrtimer_queue(struct hrtimer_base *base)
> {
> - ktime_t now = base->get_time();
> + ktime_t now = base->last_expired;
> struct rb_node *node;
>
> spin_lock_irq(&base->lock);
> @@ -594,10 +594,19 @@ static inline void run_hrtimer_queue(str
> void hrtimer_run_queues(void)
> {
> struct hrtimer_base *base = __get_cpu_var(hrtimer_bases);
> - int i;
> + ktime_t now, mono;
> + int seq;
>
> - for (i = 0; i < MAX_HRTIMER_BASES; i++)
> - run_hrtimer_queue(&base[i]);
> + do {
> + seq = read_seqbegin(&xtime_lock);
> + now = timespec_to_ktime(xtime);
> + mono = timespec_to_ktime(wall_to_monotonic);
> + } while (read_seqretry(&xtime_lock, seq));
> +
> + base[CLOCK_REALTIME].last_expired = now;
> + run_hrtimer_queue(&base[CLOCK_REALTIME]);
> + base[CLOCK_MONOTONIC].last_expired = ktime_add(now, mono);
> + run_hrtimer_queue(&base[CLOCK_MONOTONIC]);
hm, we can do this - although the open-coded loop looks ugly. In any
case, this is an optimization, and not necessary for v2.6.16. It is
certainly ok for -mm.
Acked-by: Ingo Molnar <[email protected]>
Ingo
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